1. Field of the Invention
The invention relates to a valve arrangement for a cooling system that uses a fluid that may be supercritical on the high-pressure side of the system. More particularly, the invention relates to a closed circuit refrigerating system including at least a compressor, a heat rejecting or gas cooling heat exchanger, an expansion valve, and an evaporating heat exchanger; where these elements are connected in series and the expansion valve is at least partially controlled by an electrical signal.
2. Description of Related Art
A conventional vapor compression cycle system for refrigeration, air conditioning, or heat pump purposes includes a compressor, a heat rejecting heat exchanger (gas cooler), an expansion valve, an evaporating heat exchanger (evaporator), and an accumulator. These elements are in fluid communication in a closed flow circuit, in which fluid, such as carbon dioxide (CO2), and other known fluids, is circulated. A supercritical vapor compression cycle system generally operates as follows. The compressor increases the temperature and pressure of the fluid vapor. Vapor flows out of the compressor and into the gas cooler, which then cools the fluid with the fluid giving off heat to a secondary fluid, such as air. The fluid next flows into the expansion valve, which throttles the high-pressure fluid such that the outlet fluid has a lower pressure than the inlet fluid. The low pressure fluid flows into the evaporator, which heats the fluid such that it becomes at least partially vapor. Finally, the fluid flows into the accumulator, which is used as a vapor-liquid separator, and the fluid vapor is finally drawn into the compressor, completing the cycle.
The working fluid is considered to be at a high side pressure when it is located between the outlet of the compressor and the inlet of the expansion valve. Also, the working fluid is considered to be at a low side pressure when it is located between the outlet of the expansion valve and the inlet of the compressor.
Efficiency of a vapor compression cycle is denoted as the coefficient of performance (COP) and is defined as the ratio between the refrigerating capacity and the applied compressor drive power used. In general under typical operating conditions of a supercritical system, the refrigerating capacity obtained at the evaporator rises with increasing high side pressure, and falls with decreasing high side pressure. The COP increases with increasing high side pressure up to a certain point, but then begins to decline as the extra refrigerating effect no longer fully compensates for the extra work of compression. Thus, a maximum COP can be maintained by regulating the high side pressure with the expansion valve.
The prior art expansion valve assemblies control high side pressure with an expansion valve assembly that is mechanically adjusted via a rotatable handle moving a threaded body, which in turn adjusts the position of the top of a spring. Movement of the bottom of the spring controls the size of the opening within the expansion valve and thus controls the high side pressure.
manual valve is not suitable for control of a vapor compression system as it requires human interaction to modify the setting of the valve. Obviously this is not an option for mass-produced vapor compression systems.
In view of the above, it is clear that there exists a need for an expansion valve assembly with a quick and precise response mechanism and with fewer system variables.
It is an object of the present invention to control the valve setting with an electric signal, allowing the vapor compression system to operate without human interaction, thereby making the commercial mass production of such a system feasible.
The present invention provides a refrigeration system and includes a compressor, gas cooler, an evaporator, and an expansion valve assembly. The expansion valve assembly defines an expansion chamber in fluid communication with the gas cooler, by an inlet conduit, and in fluid communication with the evaporator, by an outlet conduit. The inlet conduit contains high side pressure fluid while the outlet conduit contains low side pressure fluid. Within the expansion valve assembly, the valve position defines an opening between the expansion chamber and the outlet conduit. In one preferred embodiment of the invention, the opening is tapered. The expansion valve assembly also includes a diaphragm defining a boundary of the expansion chamber, an appendage at least partially located within the expansion chamber, and a variable-force mechanism located adjacent to the diaphragm. The variable-force mechanism is capable of downward-upward movement, and the applied force is at least partially controlled by an electrical signal correlated to the desired high side pressure.
In one preferred embodiment, a mechanical valve interfaced with a stepper motor operates as a means to achieve the desired outcome. Changes to the valve setting are quick and precise. In another preferred embodiment, the variable-force mechanism is a solenoid. In both embodiments, the appendage is at least partially controlled by the variable-force mechanism, resulting in similar possible downward-upward movement. The applied force is at least partly proportionally related to the Sigh side pressure of the system.